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Saturday, April 19, 2014

Question

How do I clean painted cinder block walls to remove oil and grime that have been exhausted from manufacturing machinery onto the walls for 20 years or so? The walls that need this cleaning are 25 ft. high, but the bad part only goes up approx. 5 ft. I have tried some industrial strength cleaners and a stiff brush, but this didnít work. I was wondering if any rental equipment such as dry ice blasting or steam cleaning would do the trick.


Answer

You have two things working against you here. The first is the age of the build-up. 20 years is long enough to allow the filth to get a really good foothold on what is a porous surface even if covered by a couple of coats of paint.
The second problem is you are obviously inside and have to control the mess.
My recommendation for this is to use a pressurized tank sprayer to apply a detergent solution (degreaser) to a small area and allow about 10 minutes of dwell time. Start at the floor and work up to avoid stubborn streaking from runs. Donít let the solution to dry, but make sure it sits long enough to penetrate the film.
Use a hot water pressure washer set at about 1500 psi to start with and work your way up the wall in the area you have pretreated.
You will likely want someone on a wet vacuum working with you to control the water coming off the wall as it runs down.
You may be able to work with a higher pressure, or you may find that the paint will run off with even a lower pressure. It is 20 years old and may have deteriorated with time.
Do a test section first.
I would not be surprised that once the wall is cleaned, it will need a repainting to make it presentable.
I have never worked with the dry ice, but I suspect it may prove too abrasive. If the above suggestion doesnít work and dry ice does, please drop us a note and tell us how things came out. Others will probably see this challenge sooner or later.

Lynn E. Krafft, ICAN/ATEX Editor
lekrafft@juno.com